Operation of radiation emitting apparatus



July 5, 1960 R. E. THORPE ET AL 2,943,986 OPERATION OF RADIATIONEMITTING APPARATUS Filed Sept. 16, 1957 ISOMERIZATION UNIT 6 INVENTORSIROY E. THORPE ALAN C "NlXO BYI 60 THEIR AGENT Unite States Patent ceOPERATION OF RADiATioN-Em'r'rm APPARATUS Roy E. Thorpe-San Francisco,and Alan C. Nixon,

Berkeley, Calif., assign'ors to Sh'ell il-Company,-a corporation ofDelaware .Filed'Sept. 16, 1957, Sex-(No. 684,222 4 Claims. cram-154perature and other eflects occurring results innumerous changes in-suchfluids such a dehydrogenation, alkylation, polymerization,decomposition, 'resinification, {isomerization, and free radicalformation. Henceg'it'is'ayserious problem to which no fully satisfactoryanswefh'as been heretofore proposed to provide'fluids are highlyresistant to radiant energy as outlined above.

Aromatic hydrocarbons -have-been proposed 'for such purposes but in manyinstances the stabilityo'f the aromatic hydrocarbons has been observedonly when they are in essentially pure form and notrnixed withpara'flins or other non-aromatic hydrocarbons. -Itha's been-found thatthe aromatics tend to alkylate under the influence of radiation (whennon-aromatics are present) and upon the formation of free radicals andwithin a relative short space of time the protective power of thearomatics is no longer present. Olefins in general have exhibitedunsatisfactory radiation stability owing to their tendency topolymerize. Aromatic compounds 'not only are fre quently of relativelyshort life in the presence of nonaromatic hydrocarbons but also aredisadvantageous when used as fuel due to their smoking and burningcharacteristics including low heat values on' a weight basis.:Co'nsequently, it is also necessary, particularly in military fuelspecifications to limit the aromatic content "to no more than about 20%by weight.

It is an object of the present invention to provide an improved processfor the operation of radiation emitting apparatus. It is a moreparticular objectof this invention to provide a process for theopera'tion of such apparatus by means of a fluid showing aminirnumdeterioration in the presence of radiant energy. It is a specialobject of the present invention to provide a means for stabilizingoperating fluids utilized in this general class of apparatus. Otherobjects willbecomeapparentduring the following discussion. Now, inaccordance with "the present invention, "it has been found thatoperating fluids for radiation emitting apparatus are especially stablewith respect to said radiation when they contain .at least 130% byweight of cis-trans isomeric cyclic (preferably polycyclic) saturatedhydrocarbons. More particularly, :a process for operating radiationemitting apparatus over .extended periods comprises utilizing:suchHfluidsas just described and recycling them "through .;a converter.efor altering the ratio of cis and trans isomers from that which2,943,986 "Patented July 5,

2 exists at the time the fluid emerges from the radiation emitting zone.

In the operation ofradiationemitting apparatus .by'the use of cyclicsaturated hydrocarbons over .an extended period an equilibrium mixtureof cis and trans isomers is created. It appears that ahig'h amount ofenergy is utilized in the transformationof cis to trans .and in thereverse reaction of transto cis isomer, although more energy appears tobe utilized inthe transformation of cis to trans. Large amounts ofenergyare. dissipated in the absorbed ionizing energy utilize d:forcis-trans isomerization. Consequently, it is possible to utilize amixture of cis-trans isomers as an operatingfluid.for-radiation emittingapparatus which is predominant'in:either cis or trans isomers since thereaction proceeds in either direction to essential equilibrium under theconditions existing, said equilibrium proceeding at a rate andto anextent specific to the conditions present and ther'particular cis-transisomers being utilized.

In the processes involving alteration of the balance of cis-transisomers in a circulating process, the alteration may be effected byeither isomerization or physical separation of the isomers existing,followed by recycling of all or a part of the products obtained'in suchprocesses. For example, if the cis-trans isomers possess melting pointsor boiling points of sufl'icient diflerence, it is possible to separatethem by means of fractional crystallization or fractional distillation.Subsequently, they may be recycled to the reactor either as ,essentiallypure cis and trans components or may be recombined in any desired ratioprior to recycling. The same is 'true of isomerization wherein theisomerizing process may result in a mixture of products, some of whichare desirable for recycling and others of which are/not. In such case,the product of the isomerizing step may be fractionated by any wellknownmeans and a desired fraction so obtained may be recycled for use as anoperating fluid in the reactor.

Still another means by whichthecis rand transisomers may be segregatedisby meansof preferential complex formation or so-called 'clathrateformation wherein relatively unstable molecular complexes .of ,aparticular compound with a clathrate-forming material isformed and thendecomposed to recover the segregated isomer which can then be recycledfor use in the radiation emitting equipment The use of cis-transsaturated polycyclic hydrocarbons for this particular purpose showsbenefits Whenathe .cistrans isomers are present to the extent of atleast 30% by weight of a given fluid, although it is preferred thatbetween about 40 and about by weight of the cis-trans isomers arepresent. Consequently, it will be seen greases, hydraulic fluids,coolants and the like may beprotected insofar as deterioration due toradiation energy byith'e presence of a minimum amount of about 30%by'weight of the cis-trans saturated cyclic hydrocarbons.

The fluids of the present invention may be utilized either in thegaseous stage or in the liquid stage orboth especially when they arebeing utilized ,as coolants. In performing this function an initiallyliquid mixture may upon absorbing-sufficient heat frorn a radiant energyreactor be converted to a gas or vapor andthereafter passed through aheat exchanger where it gives up itsthermal energy which is thenconverted in mechanical energy-Tor the operation of turbines or thelike.

The saturated cyclic hydrocarbons to be employed in accordance with thepresent invention include those capable of forming or existing as steroisomeric pairs. Prefer ably those employed have boiling points inexcessof about 'C. at atmospheric pressure and still more preferablyalsohavemelting gpoints below about 0 :C. {although the latter physicalproperty ;is not, essential for many purposes.

Table I illustrates the type of hydrocarbons which may be used but itwill be understood that this list is merely illustrative to indicate thenature of the compounds and is not regarded as restricted thereto. Thepreferred subgeneric class of compounds to be utilized in the presentprocesses include the bicyclic saturated hydrocarbons and moreparticularly, bicyclodecanes, said bicyclic hydrocarbons being eitherunsubstituted or bear- .ing alkyl substituents.

Table I [0,4,41-bicyclodecane (Decalin) l-methyl-[O,4,4]-bicyclodecane2-methyl-[0,4,41-bicyclodecane 3-rnethyl-[O,4,4]-bicyclodecane LS-dmethyl-IO,4,4]-bicycldecane 2,8-d1methyl-[O,4 41-bicyclodecanel-methyl-tethyl-(OA 41-bicyclodecane 1,5-d1methyl-8-ethyl-0,4,41-bicyclodecane 2-ethyl-3 -propy1-[O,4,4]-bieyc1odecane[0,3,4l-breyclononane [O,3,3]- b1cyclo octane2,2,4-tr1methyl-[1,1,3]-bicycloheptane (pinane) COO Thiyane Carane CFenchane O C According to the above table, it will be seen that thebicyclo alkanes are preferred due to their optimum physical propertiesparticularly when they contain at least about. 8 carbon atoms permolecule and preferably at least about 10 carbon atoms per molecule,still more preferably between about 10 and carbon atoms per molecule.The Decalins are preferred species as well as thepinanes, due to thefact that these particular materials have low melting points in theorder of to 50 C. and boiling points in the order of 165-193 C.,depending upon the rate ratio of the cis or trans isomers present.Monocycloalkanes may be utilized if they bear 2-6 alkyl substituents anda total of at least 8 carbon atoms. Such materials includetrimethylcyclohexane, diethylcyclopentane, etc. When the above types ofpolycycloalkanes are utilized in conjunction with other hydrocarbons orsubs-tituents, the resulting composition should be substantially free ofaromatics or olefins or at least should contain less than about 20% byweight thereof. Such compositions would be regarded as beingsubstantially free of olefins or aromatics when the content is less thanabout 2% by Weight thereof.

The drawing illustrates a typical process utilizing the presentinvention. In this figure a nuclear reactor 1 containing a radiantenergy producing source 2 is cooled by means of a circulatory system 3wherein a circulating .coolant fluid passes through the reactor,absorbing heat produced by the radiant energy and is passed to the heatexchanger 4, the fluid being moved by means of pump 5. Either prior toor subsequent to heat exchanging, the coolant fluid is passed through anisomerization unit 6 wherein the balance of cis and trans. isomers isaltered '4 from that contained by the coolant fluid upon its egress fromthe nuclear reactor or radiation producing zone. After alteration of theratio of cis to trans isomers in the isomerizer 6 the fluid is thenrecycled for further use as coolant in the reactor 1.

The "isomerization step per se is not regarded as a novel feature sinceisomerizing conditions are Well known in the art of treatinghydrocarbons. Consequently, it is unnecessary to present in detail thecatalysts and conditions necessary for isomerization of cis-transisomers. In general, however, isomerization is effected by the use ofaluminum halide catalysts at temperatures between about room temperatureand 250 C. for a period of time which may be momentary to about 4 days.The catalyst may contain promoters such as iron halide or hydrogenhalides and catalysts other than aluminum chloride may be utilized, suchas an alloy of nickel, cobalt and aluminum in the presence of hydrogen,or molybdenum trisulfide in the presence of hydrogen. The products ofisomerization are normally an increased amount of the trans isomer withor without other isomers being formed.

While the usual nuclear reactor contains rods or other structural unitsof the fuel, it is possible to utilize a fluidized system wherein themass of fissionable material of particles of fiuidizable size is in heattransfer relation With the heat transfer medium which may comprisepolycyclic saturated hydrocarbons such as described here inbefore. Underthese conditions, the fissionable material undergoes nuclear reactionand the energy therefrom is adsorbed by the heat transfer medium whichis then conducted to an energy transfer zone and recirculated afteralteration of the cis-trans balance as described here with for furtherheat transfer with the fluidized mass of fissionable material. Otheralterations in a typical nuclear reactor design are described by Fermiet al., U.S. 2,708,656.

The present invention may be utilized in connection with any chemical orphysical reaction being conducted in the presence of radiant energy suchas in the treatment of hydrocarbons or other oragnic compounds by theradiant energy obtained from radioactive by-products or a waste materialof atomic piles. In such instances, the organic compounds to be treatedare subjected to the radiation of spent nuclear reactive fuel elements,preferably at temperatures between about 50 and 700 F. and at radiationintensities of 50,000 to 5,000,000 roentgens per hour at pressures of525() pounds per square inch absolute and at pressures of 1-50atmospheres. The temperature range may extend to 50 F. and up to 750 F.in special instances. Atmospheres of carbon monoxide or hydrogen may beutilized or the chemical reaction may take place in the presence ofoxygen. Under such treatments, paraflins and isoparaflins may bepolymerized with concurrent hydrogenation while olefins and somearomatics are polymerized particularly if they are exposed in the vaporspace. Alkylation reactions may be conducted under such circumstances,particularly for the alkylation of aromatics. Cracking of high molecularweight materials such as petroleum residues and waxes may be effected bysuch means as well.

In the conduct of such types of reactions in the presence of radiantenergy, activating fluids may be necessary for the operation of movingmetallic parts such as pumps, hydraulic systems and the like in additionto any cooling systems which may be necessary. It is for such purposesthat the fluids of the present invention may be employed. Otherreactions which take place in the presence of radiant energy includeoxidation of hydrocarbons and halogenation thereof, particularly whenthe hydrocarbon being so treated is aromatic character.

In illustrating the stability of cis-trans saturated polycyclichydrocarbons toward radiant energy, a mixture comprising 37.7% of transDecalin, 57.5% of cis Decalin and 4.7% of tetralins, was subjected toradiant e gy i rder of 10 roentgens in a spent cobalt fuel elementinstallation. It was found that under these conditions a final ratio ofcis to trans isomer of 1.47 was obtained, only 3.9% of the productforming lower boiling materials, the product containing also 37.4% oftrans Decalin and 55.6% of cis Decalin with a reduction of tetralin to3.2%. When the resulting product is recycled to an 'isomerizing' unit toform an increased amount of the trans Decalin it can then be recycled tofurther exposure to radiant energy, the absorbed ionizing energy beingdissipated in transformation of the increased amount of trans Decalin soas to result in a product having a cis to trans ratio in the order of1.47-1.50.

When a second sample of the same components is exposed, containing 33.1%of trans Decalin, 64.2% of cis Decalin and 1.7% of tetralins, theproduct had theiollowing composition. After a dosage of 1X10 roentgensat ambient temperature, the product'c'ontained 1.2% of low boilingproducts, 39.3% of trans Decalin, 56.5% of cis Decalin, and 3%tetralins, the ratio of cis to trans Decalins in the exposed productbeing 1.44.

We claim as our invention:

1. In the operationof radiant energy-emitting equipment, wherein anoperating fluid therefor is subjected to radiation, the steps comprisingutilizing asthe operating fluid a fluid composition'comprising at least'30% by weight of cis-trans'isomeric saturated cyclic hydrocarbons,any-balance of the composition being other hydrocarbons, no more'than20% by Weight of the composition being aromatic and olefinichydrocarbons, subjecting said fluid to the radiation, 'whereby the ratioof cisisomers to trans-isomersis increased, subjecting the mix:

ture so formed to isomerizationwhereby the cisto trans ratio issubstantially decreased, and recycling the'resulting product for use asan operating fluid in radiationemitting equipment.

2. In the operation of radiant energy-emitting equipment wherein heatproduced by said energy is removed by a circulating coolant, heat soremoved being extracted from the coolant in' a heat exchanging system,the improvement comprising utilizing as said coolant a fluid comprisingabout 40-100% by weight of cisand transisomers of saturated polycyclichydrocarbons, any balance of the composition being other hydrocarbons,no more than 20% by weight of the composition being aromatic andolefinic hydrocarbons, said coolant being first subjected to radiantenergy, whereby the ratio of cisto trans-isomers reaches equilibriumunder the existing conditions, subjecting the irradiated coolant toisomerization whereupon the ratio of cisto trans-isomers is sub- 7stantially decreased, and recycling the coolant.

than 20% by weight of the composition being aromatic and olefinichydrocarbons, the ratio of cis to trans isomers being increased uponexposure to the radiant energy, circulating the exposed lubricantthrough an isomerizer, wherein the ratioof cis to trans isomers isdecreased, and circulating the lubricant back to the lubrication sites.

4. In the operation of a radiant-energy emitting power plant, wherein anoperating fluid utilized in operation of said plant is subjected toradiation emission, the improvement comprising using as said fluid afluid composition comprising at least 30% 'by weight of cisandtrans-Decalins, any balance of the composition being other hy-"drocarbons, no more than 20% by weight of the composition 'beingaromatic and olefinic hydrocarbons, the ratio of cisto transDecalin'increasing during use thereof in said plant, circulating theradiation-exposedfiuid to an isomerizer, wherein the ratio of cis totrans-Decalin is decreased, and then recycling the fluid in the opera?tion of said plant. p

" References Cited in the tile of this patent UNITED STATES PATENTSOTHER REFERENCES 8-20, 1955, vol. 7, pp. 546-555, United Nations, New

York, 1956. t I

Fermi et a1. May 17, 1955

1. IN THE OPERATION OF RADIANT ENERGY-EMITTING EQUIPMENT, WHEREIN ANOPERATING FLUID THEREFOR IS SUBJECTED TO RADIATION, THE STEPS COMPRISINGUTILIZING AS THE OPERATING FLUID A FLUID COMPOSITION COMPRISING AT LEAST30% BY WEIGHT OF CIS-TRANS ISOMERIC SATURATED CYCLIC HYDROCARBONS, ANYBALANCE OF THE COMPOSITION BEING OTHER HYDROCARBONS, NO MORE THAN 20% BYWEIGHT OF THE COMPOSITION BEING AROMATIC AND OLEFINIC HYDROCARBONS,SUBJECTING SAID FLUID TO THE RADIATION, WHEREBY THE RATIO OF CISISOMERSTO TRANS-ISOMERS IS INCREASED, SUBJECTING THE MISTURE SO FORMED TOISOMERIZATIN WHEREBY THE CIS TO TRANS RATIO IS SUBSTANTIALLY DECREASED,AND RECYCLING THE RESULTING PRODUCT FOR USE AS AN OPERATING FLUID INRADIATIONEMITTING EQUIPMENT.